Cytochrome P-450-containing mixed function oxidase is one of the major enzyme systems responsible for metabolism of xenobiotics. Chemical mechanisms for cytochrome P-450 metabolism have been investigated using correlation of Vmax and Km to Hammett's sigma parameter and Hansch's hydrophobic pi parameter. It has been found that the difference in regiospecificity in hydroxylation of monohalobenzenes by phenobarbital and beta-naphthoflavone induced microsomes is due to a difference in chemical mechanism. The electronic demand for the rate determining step for N- and O-dealkylations has been investigated using the same correlations and evidence has been obtained that supports rate limiting one electron oxidation of the amine nitrogen to the radical cation. A corresponding one election oxidation of the ether oxygen apparently does not occur.